The present invention relates to a telephone set including a circuit for seizing the line to which it is connected without lifting the handset off the gravity switch.
Normally a telephone user seizes the line to which the telephone is connected simply by lifting the handset off the telephone. This simple act operates a "gravity" switch on which the handset is supported, and contacts of the gravity switch loop the telephone line. The exchange then feeds power to the telephone via the pair of wires which also serve to convey speech and signalling such as dial pulsing. Once the line is looped so that current can flow, the telephone becomes unavailable for receiving calls from other telephones (it becomes "engaged"), and it is connected to exchange equipment for receiving instructions from the user.
Telephone sets are increasingly being equipped with electronic circuits, and in particular with microprocessors, which need to be powered from the telephone line before they can be used. However, such telephone sets include sets associated with various terminals such as telecopiers, or modems, or directory interrogation devices which may well be used without the user ever wanting to speak into the telephone. The simplest way of "turning on" a telephone set so that it can be used with such a terminal is simply to lift the handset off its gravity switch and then rest it on some other support. This solution is not entirely satisfactory: firstly there is the problem of sounds being picked up by the microphone which may be embarassing to the user or which may interfere with operation of the terminal, or both; and secondly there is a considerable risk that the user will forget to replace the handset, in which case an excessive telephone bill may result, and the telephone set and its associated terminal are prevented from receiving incoming calls, since the microprocessor is incapable of replacing the handset itself.
The present invention therefore provides a telephone set which is capable of seizing its telephone line without the handset being lifted off the gravity switch.